Large tech companies are inefficient and have very poor engineering productivity but this is largely for systemic reasons. They definitely do not have any mechanism for identifying high performers.

The basic problem they face is that they pay a fixed wage for complete IP ownership (horrible deal) and so they intentionally do not measure and reward actual performance because they do not want to compensate high performers based on the value they create.

There isn't really a solution because these companies are making rational profit maximizing decisions, it just happens that mediocrity and managed decline of locked in revenue streams is profit maximizing for them.